A typical train includes one or more locomotives, a plurality of railcars and several trainlines. The trainlines include both pneumatic and electrical lines most of which run from the lead locomotive to the last railcar in the train. One pneumatic trainline is the brake pipe. The brake pipe consists of a series of individual pipe lengths each of which secured to the underside of one railcar. Each pipe length is interconnected to another such pipe length via a flexible coupler situated between each railcar. Usually controlled so as to mimic the pressure contained in a storage tank called the equalizing reservoir, the brake pipe is thus one long continuous pipe that runs from the lead locomotive to the last railcar. The brake pipe supplies the pressurized air that is required by the brake control system to charge the various reservoirs and operate the brake control valves of each railcar in the train.
In a locomotive, the pneumatic trainlines include an actuating pipe, a main reservoir equalizing (MRE) pipe, and an independent application and release (IAR) pipe, in addition to the brake pipe. Within a locomotive consist (i.e., two or more locomotives connected together), the MRE, actuating and IAR pipes of each locomotive connect to the MRE, actuating and IAR pipes of adjacent locomotives. The IAR pipe supplies the compressed air that can be used to control the delivery of pressurized air to, and thus to operate, the air brakes of each locomotive in the train.
The brakes of a train, whether on railcars or locomotives, are applied using brake cylinders and associated components. During braking, the brake cylinders convert the pressurized air that they receive to mechanical force. From the brake cylinders this force is transmitted by mechanical linkage to the brake shoes. When the brakes are applied, it is the brake shoes that are ultimately used to slow or stop the rotation of the wheels on every vehicle in the train.
A typical locomotive has a brake control system such as any one of the various EPIC.RTM. Brake Equipment Systems produced by the Westinghouse Air Brake Company (WABCO). These brake control systems generally include a cab station unit, a keyboard, a display, a locomotive interface unit, a brake control computer and a pneumatic operating unit. The cab station unit generates various signals including those representing the positions of the automatic and independent brake handles, and conveys commands corresponding thereto to the brake control computer. The keyboard also permits a train operator to access the brake equipment, allowing, for example, the operator to input certain set-up parameters. The display allows the operation of the brake equipment to be monitored. The locomotive interface unit (LIU) connects electrical power and certain trainlines to the brake equipment and provides various signals to the brake control computer. Based on the inputs it receives and the software that dictates its operation, the brake control computer essentially controls the overall operation of the brakes. Shown in FIG. 1, the pneumatic operating unit (POU) controls the pressures in the pneumatic trainlines and in various reservoirs so as to control the brakes according to commands received from the brake control computer.
The POU features a pneumatic laminate to which the brake control computer and various pneumatically and electropneumatically operated devices mount. The design of the laminate allows these components to be removed for repair and maintenance without disturbing the piping or wiring of the locomotive. Through a number of ports and internal passages, the pneumatic laminate interconnects these devices to each other and to branch pipes that carry air from or to the actuating pipe, the MRE pipe, the IAR pipe, the brake pipe, the brake cylinder and/or various storage tanks such as the equalizing reservoir. It is through the ports and internal passages of the pneumatic laminate that these devices communicate fluidly with each other and the pneumatic pipes on the train.
Among the various devices mounted to the pneumatic laminate are the independent application and release (IAR) portion, the brake cylinder (BC) control portion and the brake pipe (BP) control portion shown in FIG. 1. These operating portions of the POU are primarily controlled by the brake control computer. The IAR portion features pneumatic logic circuitry along with solenoid operated valves by which the pressure in both the actuating and IAR pipes can be controlled. The BC control portion also features pneumatic logic circuitry along with solenoid operated valves by which the pressure in the brake cylinders on the locomotive can be controlled. The BC control portion controls the pressure in the locomotive brake cylinders in response to the commands generated by movement of either of the two brake handles. These automatic and independent brake demand signals may also be generated by pressure changes in the brake pipe, the IAR pipe, the back-up brake or the penalty brake circuitry. The BP control portion uses pneumatic logic circuitry and solenoid operated valves by which the pressure within the brake pipe throughout the entire train can be controlled. The BP control portion also controls the emergency venting and the brake pipe cut-off functions as described in further detail below.
The cab station unit generally includes a handle unit and a cab control unit. The handle unit houses the two brake handles and related components. The cab control unit essentially has a computer and a cab interface card. From the handle unit the cab control computer receives via the interface card the signals indicative of the positions of the automatic and independent brake handles. Based on these inputs, the cab control computer calculates commands representative of how much, or even if, the braking effort should be reduced. Along with other information, the cab control computer then conveys these commands to the brake control computer.
The automatic brake handle is the device that the train operator can manipulate to direct the brake equipment to apply and release the brakes on each locomotive and each railcar of the train. The level to which the brake equipment reduces or increases pressure within the brake pipe, and thus the amount of braking power exerted by the train brakes, corresponds to the position of the automatic brake handle. The independent brake handle, in contrast, allows the train operator to apply and release the brakes only on each locomotive.
The independent brake handle may be moved between and placed within any of two positions. When the independent brake handle is moved to its apply position, the brake control computer commands the IAR portion to increase pressure within the IAR pipe. The BC control portion responds pneumatically to this increase in IAR pipe pressure by directing air from the main reservoir to the brake cylinders of the locomotive to apply fully the locomotive brakes. Similarly, when the independent brake handle is moved to its release position, the brake control computer commands the IAR portion to reduce pressure within the IAR pipe. Responding pneumatically to the decrease in IAR pipe pressure, the BC control portion now vents air from the brake cylinders to release the locomotive brakes. Pressure in the IAR pipe and the locomotive brake cylinders reduces and increases in proportion to the position of the independent brake handle.
The automatic brake handle can be moved from and in between a release position at one extreme in which brake pipe pressure is maximum and the brakes are completely released to an emergency position at another extreme in which brake pipe pressure is zero and the brakes are fully applied. When the brakes are released, the equalizing reservoir and the brake pipe are generally charged to the same pressure: typically 90 psi on a freight train and 110 psi on a passenger train. When the brakes are applied, reduction of the pressure in the brake pipe is generally controlled from the lead locomotive. The exact amount by which the pressure is reduced depends into which of the application positions the brake handle is placed. It is this reduction in brake pipe pressure that signals the brake control valve on each railcar to supply pressurized air from the appropriate reservoir(s) to the brake cylinders to apply the brakes of the railcars. The automatic brake handle positions thus include release, minimum service, full service, suppression, continuous service and emergency. Between the minimum and full service positions lies the service zone wherein each incremental movement of the handle toward the full service position causes an incremental reduction in brake pipe pressure.
When the automatic brake handle is moved to its release position, the brake control computer commands the BP control portion to increase pressure within the equalizing reservoir and the brake pipe. Responding pneumatically to the resulting increase in brake pipe pressure, the brake control valves on each railcar then vent air from the brake cylinders to release completely the railcar brakes. The BC control portion also responds pneumatically to the increase in brake pipe pressure by venting air from the brake cylinders of the locomotive. Moving the automatic brake handle to its release position also causes the brake control computer to command electrically the solenoid valves of BC control portion to depressurize the locomotive brake cylinders. The BC control portion thus can release the locomotive brakes by responding to either electrical commands or pneumatic commands or both, the former issued by the brake control computer and the latter being the increase in brake pipe pressure.
When the automatic brake handle is moved to its minimum service position, the brake control computer commands the BP control portion to reduce pressure within the equalizing reservoir by approximately 6 to 7 psi, irrespective of the brake pipe pressure. This prepares the brake control system for a somewhat quicker application of the train brakes than would be possible from the release position. Moving the automatic brake handle into the service zone even up to the full service position causes the pressure in the equalizing reservoir to reduce further, though in a manner corresponding to handle position. The BP control portion reduces the brake pipe pressure accordingly thereby enabling the brake control valves on the railcars to apply the railcar brakes. Meanwhile, pressure transducers provide electrical signals indicative of the current pressures in the equalizing reservoir and brake pipe to the brake control computer. Based in part on these signals, the brake control computer then commands the BC control portion to direct air from the main reservoir to the locomotive brake cylinders to apply the locomotive brakes.
Moving the automatic brake handle beyond the full service position toward the suppression position causes no additional reduction in the pressure in the equalizing reservoir or brake pipe. When the automatic brake handle is moved beyond the suppression position, the BP control portion reduces the equalizing reservoir pressure at a service rate that corresponds approximately to handle position. Placing the automatic brake handle in the continuous service position causes the equalizing reservoir to reduce to zero at a service rate. Moving the automatic brake handle back into the service zone causes the BP control portion to assume a lap state in which the pressure within the equalizing reservoir and brake pipe is held at the existing level. The BC control portion also can assume a lap state in which the pressure in the locomotive brake cylinders can be maintained at the current pressure level.
When the automatic brake handle is moved into the emergency position, the brake equipment energizes two emergency magnet valves located in the BP control portion. Described in greater detail below, one emergency magnet valve is energized by the brake control computer whereas the other emergency magnet valve is energized directly by a microswitch that closes when the automatic brake handle is moved into its emergency position. Through these two emergency magnet valves, the BP control portion vents the brake pipe to atmosphere at an emergency rate so as to apply the train brakes quickly and fully.
Depending on which of the WABCO EPIC.RTM. Brake Equipment Systems one considers, either the keyboard or the handle unit features several keys through which the train operator can select the mode in which the locomotive is operated. In the LEAD CUT-IN mode, the brake control computer permits the locomotive operator to direct control of the train through both the automatic and the independent brake handles. This gives the operator control over the brakes of both the locomotive(s) and the railcars. In the LEAD CUT-OUT mode, the brake control computer permits the locomotive operator to direct control only through the independent brake handle. This gives the operator control over the brakes of the locomotive(s) only. In the TRAIL mode, both brake handles are rendered inoperable except for the emergency position. In a locomotive consist, the brake equipment of one locomotive operating in the TRAIL mode is essentially subservient to the brake equipment of another locomotive operating in either of the LEAD modes. As described more fully below, the operation of the BP control portion is affected by the mode in which the locomotive is operated.
The foregoing background information is provided to assist the reader to understand the invention described and claimed below. Accordingly, any terms used herein are not intended to be limited to any particular narrow interpretation unless specifically stated otherwise in this document.